Effects of side-stream operation on the mainstream biological phosphorus metabolic pathway for phosphorus recovery: Simulation by an extended ASM2d model

An extended activated sludge model (E-ASM2d) was established by including the metabolic processes of double-layer extracellular polymeric substances (EPS) and glycogen-accumulating organisms (GAOs) into the existing ASM2d model for describing and predicting the metabolic processes of the side-stream phosphorus (P) recovery reactor. A sensitivity analysis of model parameters on S_PO4(soluble phosphate), X_LEPS (loosely-bound EPS), X_TEPS (tightly-bound EPS), COD, and S_NH4 (soluble ammonia nitrogen) outputs was conducted for identifying influential parameters. The predicted effluent values of COD, ammonia nitrogen (NH₄), and P corresponded well with actual measured values and all the model performance coefficient values for COD, NH_4, and P were higher than 0.65, implying the E-ASM2d model could accurately simulate the metabolic processes of the side-stream P recovery process under different COD:P ratio conditions. The variations in the mainstream biological P metabolic pathway under different COD:P conditions were investigated by the E-ASM2d model. At COD:P ratios of 30, 20, and 10, the values of f_PP,TEPS (fraction of X_TEPS in polyphosphate metabolic process) increased from 0.092, 0.094, and 0.096 in the initial phase to 0.107, 0.124, and 0.187 in the side-stream phase, respectively, demonstrating that the fraction of P removal by tightly-bound EPS was improved by the side-stream operation.